Memory devices may be provided as integrated circuits in computers or other electronic devices. There are many different types of memory devices, and memory devices may generally be volatile or non-volatile. Volatile memory may require power to maintain information stored therein, while non-volatile memory may not lose the stored information in the absence of power. Examples of volatile memory include DRAM and SDRAM memory devices. Examples of non-volatile memory include ROM, flash memory, and resistance variable memory. With increasing popularity of electronic devices, such as laptop computers, portable digital assistants, digital cameras, mobile phones, digital audio players, video game consoles and the like, demand for nonvolatile memories are considered to be on the rise.
Examples of resistance variable memory, a type of non-volatile memory, include phase change memory (PCM) devices. A phase change memory cell layout may resemble that of a DRAM memory cell, with the DRAM capacitor being replaced by a phase change material, such as Germanium-Antimony-Telluride (GST). The phase change material, e.g. GST, may exist in two states—an amorphous, high resistance state, or a crystalline, low resistance state. The resistance state of the material may be altered by applying current pulses to the cell, for example by heating the material with a programming current. In this manner, a PCM memory cell may be programmed to a particular resistance state through use of a programming current. In some examples, the amorphous, high resistance state of the material in the memory cell may correspond to a logic state of 1, while the crystalline, low resistance state of the material in the memory cell may correspond to a logic state of 0. In other examples, the opposite logic assignments may be used.
The programmed resistance state of a PCM cell may be determined by sensing a current and/or voltage associated with the cell. During a sensing operation, e.g. a read operation, a sensed voltage and/or current associated with the PCM cell may be compared with one or more reference voltages and/or currents to determine the particular state of the PCI cell.